Insight into the synergistic effect on adsorption for Cr(VI) by a polypyrrole-based composite

Polypyrrole-based (PPy) composite are promising candidates for the treatment of water pollution. Adsorption selectivity as well as a large adsorption capacity are two key factors for treating wastewater containing multiple ions. The structure and morphology of the prepared composites were characterized by the FT-IR, XRD and SEM examinations. The results indicate that the Fe3O4 and PPy nanosphere coats attapulgite (ATP) closely and evenly. Herein, a novel Fe3O4 and ATP doped three-dimensional network structure PPy/Fe3O4/ATP composite was demonstrated as an excellent adsorbent to effectively remove Cr(VI). The as-synthesized PPy/Fe3O4/ATP composite is suitable for Cr(VI) adsorption in a wide pH range (pH 2–6). Up to a 96.44% removal rate was found with 400 mg L−1 Cr(VI) aqueous solution in 30 min for 0.2 g PPy/Fe3O4/ATP adsorbent. Adsorption results showed that Cr(VI) removal efficiency by PPy/Fe3O4/ATP decreased with an increase in pH. The removal rate of Cr(VI) had already reached 93.63% in 15 min contact time. Co-existing ions studies exhibit inorganic oxyacid anion and transition metal cation showed negative effects on Cr(VI) removal rate. A chemical rather than a physical adsorption occurred for these adsorbents as revealed by a pseudo-second-order kinetic study. The results of the adsorption isotherms showed that the adsorption process was similar to the Langmuir isotherm adsorption. Furthermore, the PPy/Fe3O4/ATP composite exhibited a high stability for Cr(VI) adsorption during recycling tests process. This work may provide some useful guidelines for designing adsorbents with selectivity toward specific heavy metal ions.