Functional Polymers and Polymer-Clay Nanocomposite for Oxyanions Removal

摘要

Polymer-clay nanocomposites researches have presented a great attention from scientific community because nanocomposite materials present enhanced properties (mechanical, thermal, and barrier properties) compared with starting material (unloaded polymers). In case of crosslinked hydrophilic materials such as hydrogel and superabsorbent materials, the addition of clay could potentially result in either an increase or a decrease in the water absorbency. In this work, we present the study of the characterization and adsorption properties of polymer-clay ion exchange resins, which are based on a polymer matrix bearing functional groups able to interact with oxyanions (quaternary ammonium groups), and layered double hydroxide (LDH) dispersed within the resin. These positive charged clays allow its usage as anion exchange materials, such as oxyanions. Membrane filtration allows easily the separation of ions bound to water-soluble polymers from non-bound ions. The process involves the simultaneous use of a ultrafiltration membrane and water-soluble polymers (WSP), having functional groups which interact with the ionic species of low molecular weight, forming a "polymer-anion" which cannot pass through the membrane. Through to washing method, the Cr(Ⅵ) and As(Ⅴ) removal experiments were carried out at different pH (3, 6 and 9) using WSPs containing quaternary ammonium salts with chloride or methylsufate counterions. The results showed highest retention capacity of Cr(Ⅳ) and As(Ⅴ) at pH 9. The retention capacity in both cases was optimum for polymers containing chloride counterions. The removal properties of functional polymers containing ammonium groups were also studied for molybdate and vanadate anions under different experimental conditions. The removal ability depended strongly on the pH and on the oxyanion. The removal behaviour under competitive conditions was carried out.