3D cryogel filters as colorimetric indicators of mercury and simultaneous wastewater remediation

This work presents the development of a functional hydrogel for simultaneous water treatment and quality monitoring. This was achieved by decorating poly (sodium acrylate) (PSA) cryogels with silver nanoparticles, grown in situ within the polymer matrix. The resulting materials effectively purify wastewater through gravity driven filtration, and at the same time act as colorimetric indicators of mercury ions. The composite cryogels were prepared by loading PSA with silver ions through dipping in aqueous solutions, followed by in situ chemical reduction to silver nanoparticles of mean size of 25 ± 14 nm. This process resulted in brown-colored, 3D porous composites, due to the silver nanoparticles’ presence in the polymer matrix. The nanocomposite cryogels were successfully employed for gravity driven purification of various metal ion-loaded water solutions, as they sorb effectively all the pollutants tested, reaching separation efficiencies higher than 90% for all metals (for 5 ppm initial concentration each), with simultaneous color shift from brownish to whitish only in the presence of mercury ions, indicating their effective interactions with silver due to the amalgamation process. Through detailed studies we prove that the composite cryogel sorbs up to 384 ± 10 mg/g of mercury ions for the maximum concentration of 100 ppm in the feed solution tested, while their color is altered with mercury concentrations as low as 0.5 ppm under the specific experimental conditions. Taken together, these findings demonstrate that the presented PSA-silver nanoparticle composites are promising candidates for both metal ions removal and trace mercury detection in wastewater treatment. • Silver nanoparticles were grown in situ in a poly sodium acrylate cryogel. • The composite cryogel becomes brown after the functionalization. • The composite sorbs metal cation contaminated water via gravity driven filtration. • The composite changes color, from brown to transparent, in the presence of Hg 2+ . • Purification and selective Hg 2+ colorimetric detection occur in a single step.