A review of polyampholytic ion scavengers for toxic metal ion removal from aqueous systems

Abstract

Pollution by heavy metal ions in aqueous systems gained researchers attention gradually. Toxic metal ions were always present in the environment and the living organisms could get used to specific concentrations of contaminants with given time, however, sudden concentration rise we are observing can make it impossible for the living organisms to adapt. Many ion removal technologies were developed and optimised over the years to cope with this problem, including chemical precipitation, adsorption, membrane filtration and ion-exchange. Adsorption and ion exchange are processes that employ certain materials, that can be collectively named ion scavengers, to remove ions from aqueous solutions. Some of the scavenger materials are still barely studied, in particular polyampholytes - polymeric zwitterionic materials. This review showcases papers published on toxic metal ion removal by polyampholytes, both commercial and experimental, over last two decades. Many recent publications show promising properties of experimental materials that match or even outperform commercial scavengers. This review was prepared to encourage other researchers to investigate this broad and still not well-studied class of materials especially in context of their ion-scavenging properties. Polyamphytes which may be especially worth the attention and further research have been highlighted as literature studies show that the most unexplored materials in the class of polyamphytes are those containing aminomethylphosphonate, aminomethylsulfonate or hypophosphorous acid group.

Keywords: Adsorption; Ion exchange; Ion scavengers; Metal ion removal; Polyampholytes; Toxic metal ions.