Chemically Modified Chicken Feather as Sorbent for Removing Toxic Chromium(VI) Ions

To improve the sorption capacity of Cr(VI) ions, chicken feathers (CFs) were chemically treated by several methods: (1) To clarify the changes in the structure and morphology of CFs, CFs were treated with aqueous NaOH solutions of varying concentrations. The results suggest that reactions occur on the surface rather than in the interior of the CFs and that keratin fragments exfoliate from the CF surface layer by layer and then dissolve in aqueous solution. (2) Keratin fragments could be rejoined to the CF surface by cross-linking with epichlorohydrin (Epi) through a series of ring-opening, recyclization, and ring-opening reactions of Epi in aqueous NaOH solution, and Epi-modified CF (EpiCF) was obtained. (3) CFs were functionalized with ethylenediamine (EA) in aqueous NaOH solution by cross-linking with Epi (EAEpiCF). The structure and properties of chemically treated CFs were investigated by FT-IR spectroscopy, XRD, SEM, elemental analysis, and water contact-angle measurements. CFs treated with NaOH were found to be similar in structure and properties to each other and exhibited a relatively low sorption capacity for removal of Cr(VI) ions from water, but a higher capacity than raw CFs. EpiCF exhibited an excellent capacity for adsorbing relatively low concentrations (10 ppm) of Cr(VI) ions but a low sorption capacity for Cu(II) ions in water. EAEpiCF was found to be hydrophilic and to exhibit 90% efficiency for removing Cr(VI) ions in the concentration range of 10−80 ppm but to have a low sorption capacity for Cu(II) in water. Equilibrium sorption isotherms for the raw and chemically treated CFs fit the Freundlich and Dubinin−Radushkevich (D−R) isotherm models; however, the Langmuir model was not able to describe the sorption behavior. The values of the free sorption energy (E) were calculated. The E values of NaOH-treated CFs were found to be similar to each other and much larger than that of raw CFs for the sorption of Cr(VI), and the sorption processes were found to be physical. The process of EpiCF adsorbing Cr(VI) ions from water is chemisorption, and that for Cu(II) ions is physisorption. The free sorption energy of EAEpiCF sorption of Cr(VI) ions was close to 8 kJ·mol−1 (7.274 kJ·mol−1), so that chemical interactions might exist between EAEpiCF and Cr(VI), whereas for Cu(II), the sorption process is physical adsorption.