An XPS study of chromate and vanadate sorption mechanism by chitosan membrane containing copper nanoparticles

• Chitosan (CHI) as support for copper nanoparticles (Cu-NPs).
• Application as sorbent of Cr(VI) and V(V) dilute solutions.
• X-ray Photoelectron Spectroscopy (XPS) analysis.
• Investigation of the sorption mechanism.

Chitosan (CHI) membrane containing copper nanoparticles (Cu-NPs) is a potential sorbent for chromate and vanadate removal from aquatic environment. X-ray photo-electron spectroscopy (XPS) was employed to investigate the influence of Cu-NPs on Cr(VI) and V(V) sorption processes. XPS is a powerful technique to understand the mechanisms involved in metal binding to the polymer. X-ray Diffraction (XRD) and Transmission electron microscopy (TEM) confirmed the Cu-NPs presence inside CHI membrane. XPS spectra obtained after sorption showed that Cr(VI) and V(V) ions interact differently with CHI membrane containing Cu-NPs, although both species have similar reduction potentials: Cr(VI)/Cr(III), E0 = +1.33 V and V(V)/V(IV), E0 = +1.00 V against Cu(II)/Cu(I), E0 = +0.16 V. Cr(VI) was reduced to Cr(III) while Cu(I) was oxidized to Cu(II). On the other side, in the case of vanadate sorption, the interactions between vanadate species and CHI amine groups were more significant than the redox reactions involving copper.