Highly efficient detoxification of Cr(VI) by chitosan-Fe(III) complex: process and mechanism studies

Metal-biopolymer complexes has recently gained significant attention as an effective adsorbent used for the removal of Cr(VI) from water. Unfortunately, despite increasing research efforts in the field of removal efficiency, whether this kind of complex can reduce Cr(VI) to less-toxic Cr(III) and what are the mechanisms of detoxification processes are still unknown. In this study, despite the highly adsorption efficiency (maximum adsorption capacity of 173.1 mg/g in 10 min), the significant improvement of Cr(VI) reduction by chitosan-Fe(III) complex compared with normal crosslinked chitoan has been demonstrated. In addition, the structure of chitosan-Fe(III) complex and its functional groups concerned with Cr(VI) detoxification have been characterized by the powerful spectroscopic techniques X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS). The XPS spectra indicated that the primary alcoholic function on C-6 served as an electron donor during Cr(VI) reduction and was oxidized to a carbonyl group. The X-ray adsorption near edge spectra (XANES) of the Cr(VI)-treated chitosan-Fe(III) complex revealed the similar geometrical arrangement of Cr species as that in Cr(III)-bound chitosan-Fe(III). Overall, a possible process and mechanism for highly efficient detoxification of Cr(VI) by chitosan-Fe(III) complex has been elucidate.