Effective removal of Cr(VI) in water by bulk-size polyaniline/polyvinyl alcohol/amyloid fibril composite beads

Abstract

With the rapid expansion of industrial activities, chromium ions are discharged into the environment and cause water and soil pollution of various extents, which seriously endangers the natural ecological environment and human health. In this study, polyaniline/polyvinyl alcohol/amyloid fibril (PANI/PVA/AFL) composite gel beads (PPA) were prepared from polyaniline and amyloid fibrils with HCl as doping acid and PVA as a cross-linking agent. The results showed that PPA was an irregular composite bead with a diameter of 6 mm. The adsorption of Cr(VI) on the PPA gel beads followed the pseudo-second-order kinetics model, suggesting that chemical reactions were the controlling step in the Cr(VI) adsorption process. Though the Redlich–Peterson isotherm model had the best fit for the adsorption data, the isothermal adsorption process can be simplified using the Langmuir model. The maximum adsorption capacity for Cr(VI) in water was 51.5 mg g−1, comparable to or even higher than some PANI-based nanomaterials. Thermodynamic parameters showed that the adsorption process was a spontaneous, endothermic, and entropy-increasing process. Microscopic analysis revealed that the capture of Cr(VI) on PPA was mainly governed by electrostatic attraction, reduction, and complexation reactions. PPA can be used as a kind of effective remediation agent to remove Cr(VI) in water. HIGHLIGHTS PPA gel beads with bulk sizes were synthesized to remediate Cr(VI) in water.; Adsorption kinetics, isotherms, and thermodynamics of Cr on the PPA gel beads were studied.; PPA showed a high adsorption capacity (51.5 mg g−1) for Cr(VI).; Cr(VI) was almost completely reduced to Cr(III) on the PPA beads.; Electrostatic attraction, reduction, and complexation occurred for the Cr(VI) removal.;

Keywords

• adsorption
• amyloid fibril
• chromium
• polyaniline
• redox reaction