Characterization of exopolysaccharides after sorption of silver ions in aqueous solution

• Ag+ biosorption by four EPS differing from each other in their chemical composition.
• XPS, FTIR, XRD, TEM were applied to characterize the EPS before and after sorption.
• The role of sulphate groups in the biosorption is highlighted.
• Silver and silver oxide nanoparticles were observed.

Biosorption of silver ions by several exopolysaccharides (EPS) differing from each other in their chemical composition and functional groups was investigated. EPS were characterized before and after Ag(I) biosorption by comprehensively using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, transmission electron microscopy (TEM). The role of the different functional groups in the biosorption process was observed. In particular, sulfate groups were seen playing a major role. XPS and FTIR methods showed that the composition of lowest efficient EPS changed after Ag(I) biosorption with a relative increase of the carboxylate ions content. This change was accompanied by the formation of mainly silver oxide nanoparticles. As the consequence, the reducing character of the EPS is expected to influence the silver sorption capability of the EPS.

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