High efficient adsorption accompanied by in-situ reduction of Cr(VI) removal by rice straw fiber ball coated with polypyrrole

Abstract

Rice straw fiber ball coated with polypyrrole (PPy-SFB), a novel adsorbent, was prepared from waste rice straw through in-situ oxidative polymerization of pyrrole monomer. The Cr(VI) adsorption characteristics of PPy-SFB were investigated not only in batch experiments but also in the column experiments, the isothermal models (Langmuir, Freundlich and Temkin), the kinetic models (Pseudo-first-order kinetic, Pseudo-second-order kinetic and Intra-particle diffusion models), and the dynamic models (Adams-Bohart, Thomas and Yoon-Nelson) were used to describe the adsorption behavior. The Cr(VI) removal mechanism of PPy-SFB was revealed by studying the effect of pH on adsorption, testing of Cl−, and analyzing the XPS. The results showed that PPy-SFB could efficiently adsorb and reduce Cr(VI) from water, and the maximum adsorption capacity reached 122.15 mg g−1 at 30 ℃ and pH = 3.0. Adsorption of Cr(VI) by PPy-SFB followed the Langmuir isotherm model, Pseudo-second-order kinetic model and Yoon-Nelson model. The thermodynamic parameters (ΔG0 < 0, ΔH0 > 0 and ΔS0 > 0) indicated that the adsorption process was endothermic and spontaneous in nature. The electrostatic interaction, ion exchange between Cl− and Cr(VI), and reduction of the PPy-SFB surface were attributed to the high efficient removal of Cr(VI). In addition, the adsorbed Cr(VI) was recovered in the form of pure Cr2O3 by simple incineration.