Why Natural or Electron Irradiated Sheep Wool Show Anomalous Sorption of Higher Concentrations of Copper(II)

Abstract

Sorption of higher concentrations of Cu(II) solution onto natural sheep wool or wool irradiated by an electron beam was studied. Sorption isotherms were of unexpected character, showing extremes. The samples with lower absorbed doses adsorbed less than non-irradiated wool, while higher doses led to increased sorption varying with both concentration and dose. FTIR spectra taken from the fibre surface and bulk were different. It was concluded that there was formation of Cu(II)-complexes of carboxylic and cysteic acids with ligands coming from various keratin macromolecules. Clusters of chains crosslinked through the ligands on the surface limit diffusion of Cu(II) into the bulk of fibre, thus decreasing the sorption. After exhausting the available ligands on the surface the remaining Cu(II) cations diffuse into the keratin bulk. Here, depending on accessibility of suitable ligands, Cu(II) creates simple or complex salts giving rise to the sorption extremes. Suggestion of a mechanism for this phenomenon is presented.

Radiation-modified wool for adsorption of redox metals and potentially for nanoparticles

“…As results from Table 2, all doses show strictly linear courses of the function differing in the position of the intersection with Figure 1 copying their shape since the slopes ( Table 2) are practically the same for all doses. These results confirm our previous findings [32] on the dependence of atypical adsorption character of Cu(II) on wool on the absorbed dose, concentration and variability of the Cu-complexes.…”

“…Applying higher Cu(II) concentrations in the range of about 800-5,000 mg/L (12.5-80 mmol/L) under adsorption on the electron-irradiated wool with various absorbed doses, we observed unexpected results showing extremes [32]. Till this time, any similar fact is not described in scientific sources.…”

“…The Langmuir model is generally suitable for lower adsorbate concentrations, which is not quite well fulfilled in our case. As shown, the Cu(II) at a sufficient concentration very readily forms complexes with the ligands provided by keratin, immediately on the surface of the fibre [32]. Since the initial content of the carboxyl groups in keratin is higher than that of the amino groups [18], some parts of the complex molecule have to be ligands coming from several keratin chains, thus forming crosslinks.…”

“…This also indicates the course of sorptivity for Cu(II) on the different dosed wool (Figure 1), which shows atypical fluctuation in the range of the applied concentrations. Indeed, the formation of the Cu(II) complexes with wool was proven using FTIR and ATR spectroscopy [32]. As found, Cu(II) complexes often exhibit a distorted tetrahedral or octahedral structure [34].…”

“…With some simplification and based on papers [32,[34][35][36], we can assume that the reasons are as follows: (a) double Cu(II)-salts (carboxylates and cysteinates) bound to different side branches of keratin chain, (b) several types of potential ligands (amines, imines, hydroxyls, sulfhydryls), (c) the ability of Cu(II) to form several geometric structures of the complexes, including degenerates depending on the ligand availability and the spatial possibilities on the surface and in subsurface layers of the fibre. Such combined circumstances can hardly be fully covered by a single model.…”