Local Atomic Structure and Magnetic Ordering of Iron in Fe−Chitosan Complexes

Abstract

The iron crosslinked chitosan (Ch-Fe-CL) and N-carboxylmethyl chitosan (N-CM-Ch-Fe) complexes were studied by complementary techniques: structurally sensitive Mössbauer and X-ray absorption methods, as well as static magnetic measurements. A detailed and consistent description of these complexes including, besides the overall magnetic behavior, the spin ordering and local atomic structure around Fe ions is presented. Fe atoms in the investigated samples are mostly penta-coordinated and appear in a high spin Fe (3+) ionic state. In Ch-Fe-CL, two kinds of Fe near neighbors are equally probable and several Fe atoms are situated in the second coordination sphere. The magnetic interactions between these Fe ions lead to a sperimagnetic-like ordering. In N-CM-Ch-Fe, only one Fe neighborhood was found. Other Fe atoms were identified neither in the first nor in the second coordination sphere, but the third coordination sphere indicates the presence of Fe atoms. The magnetic coupling between these atoms is antiferromagnetic, but the dominant part of Fe in this sample remains in a paramagnetic state.

Utilization of diatomite/chitosan–Fe (III) composite for the removal of anionic azo dyes from wastewater: Equilibrium, kinetics and thermodynamics

“…The adsorbent was prepared by a modified literature procedure [1,19]. First, chitosan powder (1.0 g) was dissolved in 0.2 M FeCl 3 aqueous solution (50 mL).…”

Iron location in O-carboxymethyl chitosans determined by X-ray absorption spectroscopy

“…Our previous studies of the N-carboxymethyl chitosan and the Fe cross linked chitosan demonstrated the usefulness of XAFS in obtaining information about the location of iron atoms in these disordered systems [12]. As a result of the performed studies the 'pendant' model of iron bonding proposed in the literature [15] was excluded and the 'bridge or chelate' model was confirmed.…”

“…This parameter is directly correlated with coordi- nation number (N), and must be evaluated separately if N is unknown. S 2 0 was estimated using the procedure described in reference [12]. The estimated value in this case was S 2 0 = 0.65 ± 0.05 which, according to reference [11], is acceptable.…”

“…It is an ideal tool for getting information about the average radial distribution of the near neighbour atoms around Fe in chitosans and thus clarifying the binding mechanism of Fe [11]. Our previous XAFS studies of the Fe cross-linked chitosan and the N-carboxymethyl chitosan with Fe allowed us to determine local atomic order around Fe ion in these disordered materials up to the third coordination sphere [12]. In the presented Letter XAFS studies of O-carboxymethyl chitosans with Fe are reported.…”

Environmental Applications of Chitosan and Its Derivatives

“…Metal ions are coordinated to the -NH 2 groups of chitosan to form a pendant-like metal-chitosan complex (Lü et al 2008). The stability of metal-chitosan complexes is further enhanced by chelation, whereby the metal ion is coordinated to two -OH groups and two -NH 2 groups to form a bridge-like metal-chitosan complex (Klepka et al 2008).…”