Dual-Responsive Hydrogels for Mercury Ion Detection and Removal from Wastewater

This study describes the development of a fast and cost-effective method for the detection and removal of Hg²⁺ ions from aqueous media, consisting of hydrogels incorporating chelating agents and a rhodamine derivative (to afford a qualitative evaluation of the heavy metal entrapment inside the 3D polymeric matrix). These hydrogels, designed for the simultaneous detection and entrapment of mercury, were obtained through the photopolymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) and N-vinyl-2-pyrrolidone (NVP), utilizing N,N'-methylenebisacrylamide (MBA) as crosslinker, in the presence of polyvinyl alcohol (PVA), a rhodamine B derivative, and one of the following chelating agents: phytic acid, 1,3-diamino-2-hydroxypropane-tetraacetic acid, triethylenetetramine-hexaacetic acid, or ethylenediaminetetraacetic acid disodium salt. The rhodamine derivative had a dual purpose in this study: firstly, it was incorporated into the hydrogel to allow the qualitative evaluation of mercury entrapment through its fluorogenic switch-off abilities when sensing Hg²⁺ ions; secondly, it was used to quantitatively evaluate the level of residual mercury from the decontaminated aqueous solutions, via the UV-Vis technique. The ICP-MS analysis of the hydrogels also confirmed the successful entrapment of mercury inside the hydrogels and a good correlation with the UV-Vis method.