Biosorbent derived from plant tannin for selective removal of Cu(II) from aqueous solutions at low concentration

Despite the low levels of copper ions in aquatic environments, excessive concentrations of copper ions can eventually cause serious harm to animals and humans as they are biologically enriched and ecologically cycled. Herein, an appropriate and selective separating material for copper ions with low concentrations needs to be developed. In the present work, bayberry tannin-modified chitosan fibres (TMF) were fabricated for selective removal of Cu2+. The adjacent phenolic hydroxyl groups at the B ring of tannin enable them to chelate with heavy metal ions, while the fibre structure of chitosan is conducive to the extended distribution of the active sites. It showed an adsorption capacity of 14.98 mg g-1 for Cu2+ at 303 K, which was higher than that of most conventional adsorbents and activated carbon. Moreover, in the presence of co-existing heavy metal ions, including Ni2+, Cd2+, Fe3+ and Cr3+, we found that TMF showed highly selective adsorption of Cu2+, with Cu2+ concentrations as low as 5 mg l-1. The TMF can be robustly recycled through acid treatment with 96.6% desorption efficiency.