An X-ray photoelectron study of the interaction of uranyl group with sulfosuccinyl chitosan

Abstract

Interaction of uranium with low-molecular-weight sulfosuccinyl chitosan (SSLMWC) from sulfate solutions was studied by X-ray photoelectron spectroscopy. The interaction involves formation of complexes with the uranyl group on the SSLMWC surface. The equatorial plane of these complexes can contain nitrogen atom of the amino group and oxygen atoms of the sulfato and sulfo groups SO 4 2-and -SO 3 H, carboxy groups, and free hydroxy groups. On keeping the complex in a vacuum, two chemically nonequivalent states of U ions, U 4+ and UO 2 2+ , are observed. The U 4+ formation in solid U-containing samples of chitosan and SSLMWC is attributed to the radical reaction of the UO 2 2+ reduction with the primary hydroxy group of chitosan in a vacuum of the spectrometer under the action of X-ray radiation.Recently there has been a great deal of interest in sulfo derivatives of chitosan, which is due to the discovery of new kinds of their biological activity in combination with low toxicity. Furthermore, the presence of sulfo groups in chitosan can alter its physicochemical properties and enhance the ability to form complexes with metal ions.In [1] we examined the effect of low-molecularweight sulfosuccinyl chitosan (SSLMWC) on the stability of a 5 × 10 -3 M aqueous solution of UO 2 SO 4 in the pH range 1-10. We showed that, at the SSLMWC content lower than 2.5 g l -1 , hydrolyzed UO 2 2+ species precipitated fully or partially. At SSLMWC concentrations of 2.5 g l -1 and above, uranium was quantitatively retained in the solution for 200 days. This stability suggested formation of a stable complex. It was confirmed by differences in the absorption spectra of UO 2 SO 4 solutions in the presence of SSLMWC and without it. With SSLMWC, the absorption band splitting characteristic of UO 2 SO 4 solutions was not observed. The maximum observed at λ = 414 nm underwent red shift in the course of solution storage.Unfortunately, there is still no common opinion on the character of the interaction of UO 2 2+ with chitosan. Piron and Domard [2] made assumptions on the composition of the UO 2 2+ chitosan complex. In their opinion, UO 2 2+ is surrounded by two hydroxy groups and one amino group, and also by the water molecule or hydroxy group at the С3 atom of the glucopyranose ring. Similar results were obtained in [3].In this work we studied by X-ray photoelectron spectroscopy (XPES) the interaction of UO 2 2+ with SSLMWC in comparison with the starting polymer containing unsubstituted amino groups.