Enhanced Iodide Removal from Water by Nano-Silver Modified Anion Exchanger

Water contamination by iodide has attracted much public attention in recent years due to its impact on public health. In this work, a novel sorbent Ag-D201 was synthesized by modifying a strong anion exchanger with nanosilver particles for selective iodide removal from water. Batch adsorption tests showed that, at neutral pH, Ag-D201 had a maximum iodide adsorption capacity of 312.5 mg/g. Solution pH had no obvious influence on iodide adsorption by this material in the pH range of 3-8, although further increase in solution pH would cause slight inhibition of iodide removal. Further experiments indicated that the material exhibited improved iodide removal selectivity in the presence of commonly encountered anions SO42-, NO3-, HCO3- and Cl- compared with its counterpart. At 500 mM chloride concentration (about 0.56 M Cl- in seawater), Ag-D201 still achieved more than half of its capacity as compared to control. A synergistic adsorption mechanism was proposed after analyzing the data from batch experiments and material characterizations using XPS and UV-vis. It was speculated that Ag-D201 synthesized in this study possessed two types of active sites for iodide adsorption, -N+(CH3)(3) functional groups originally from the unmodified strong anion exchanger and the nanosilver particles impregnated in the resin matrix. The -N+(CH3)(3) functional groups served to concentrate iodide from bulk solution to resin pores through electrostatic interaction, and nanosilver particles inside the resin pores attracted the neighboring iodide due to strong nucleophilic interaction between I- and Ag(0 )The appearance of strongly nucleophilic I- on silver surfaces helped to catalyze Ag oxidation by dissolved oxygen in solution, and eventually forming AgI precipitate, causing iodide removal from the system. This material would be potentially useful in treating iodide-contaminated water caused by accidental spills of high salinity water like that from deep geological formations during shale gas extraction.