Cryogel-based Ag°/Ag₂O nanocomposites for iodide removal from water

In this study novel silver-modified cryogels were synthesized and applied for the removal of iodide from aqueous solutions. The co-allylamine-methacrylic acid-DMAAm-BisAAm (AAC) and co-allylamine-2-acrylamido-2-methyl-1-propansulfonic acid-DMAAm-BisAAm (SAC) cryogels were decorated with silver by one-step ion-exchange technique and characterized by TEM/EDS, SEM/EDS, FT-IR, XRD and zeta potential measurements. The silver loading was up to 159 and 98 mg/g for AAC and SAC cryogel nanocomposites, respectively. The silver is found in the structure of cryogels in the form of Ag₂O and Ag° nanoparticles and the formation of metallic silver is attributed to in situ reduction of silver by the functional groups of the cryogels. The nanocomposites showed rapid kinetics and high adsorption capacity towards iodide. The equilibrium studies showed that in some samples the removal of iodide is higher than the theoretically expected based on the Ag:I molar ratio of 1:1. The analysis of the surface of the cryogels confirmed the theoretical Ag:I molar ratio and a study of the solution phase revealed that small amounts of leached Ag⁺ from the cryogels resulted in the formation of AgI colloids which, under the conditions of the experiments, exhibit Ag:I molar ratios lower than the theoretical value explaining the discrepancies between the theoretical and actual iodide removal rates.