Copper, mercury and chromium adsorption on natural and crosslinked chitosan films: an XPS investigation of mechanism

Abstract

Although biopolymers are focusing the attention of researchers as potential adsorbents for heavy metal removal, little information is given about the properties of the resulting complexes. This information would also bring a better understanding of the mechanisms involved in metal binding to the poly-mer. XPS (X-ray photo-electron spectroscopy) is a powerful technique to investigate how metal ions bind onto these matrices. In this study, copper, chromium and mercury ions were adsorbed on natural and crosslinked (glutaraldehyde and epichlorohydrin) chitosan matrices, which present diverse functional groups and may induce different adsorption mechanisms. X-ray photoelectron spectroscopy (XPS) revealed that these metals bind to glutaraldehyde-crosslinked chitosan, differently from the other two kinds of matrices. Hence, amino group availability and the formation of new structures such as imino bonds are key factors. Copper(II) stabilization was found to be poor in glutaraldehyde-crosslinked chitosan. Conversely, Hg(II) ions present higher adsorption capacity in this kind of matrix. Chromium(VI) was reduced in all three matrices. In this case, chromium(VI) is probably not well stabilized by the functional groups of these polymers and may also undergo the action of their reducing groups.