Removal of iodide anions in water by silver nanoparticles supported on polystyrene anion exchanger.

The removal of iodide (I-) from source waters is an effective strategy to minimize the formation of iodinated disinfection by-products (DBPs), which are more toxic than their brominated and chlorinated analogues. In this work, a nanocomposite Ag-D201 was synthesized by multiple in situ reduction of Ag-complex in D201 polymer matrix, to achieve highly efficient removal of iodide from water. Scanning electron microscope /energy dispersive spectrometer characterization showed that uniform cubic silver nanoparticles (AgNPs) evenly dispersed in the D201 pores. The equilibrium isotherms data for iodide adsorption onto Ag-D201 was well fitted with Langmuir isotherm with the adsorption capacity of 533 mg/g at neutral pH. The adsorption capacity of Ag-D201 increased with the decrease of pH in acidic aqueous solution, and reached the maximum value of 802 mg/g at pH 2. This was attributed to the oxidization of I-, by dissolved oxygen under the catalysis of AgNPs, to I2 which was finally adsorbed as AgI3. However, the aqueous solutions at pH 7 - 11 could hardly affect the iodide adsorption. The adsorption of I- was barely affected by real water matrixes such as competitive anions (SO42-, NO3-, HCO3-, Cl-) and natural organic matter, of which interference of NOM was offset by the presence of Ca2+. The proposed synergistic mechanism for the excellent performance of iodide adsorption by the absorbent was ascribed to the Donnan membrane effect caused by the D201 resin, the chemisorption of I- by AgNPs, and the catalytic effect of AgNPs.