Nanopore-Based Strategy for Sequential Separation of Heavy-Metal Ions in Water

Developing novel methods for the removal of heavy-metal ions from wastewater with low costs, special selectivity and high efficiency is quite important in water restoration and comprehensive ecological improvement. In this work, a nanopore-based strategy was suggested and related segregation apparatus was built to separate multiple heavy-metal ions in water by selective complexation. The results indicated that the prioritization of the selecting order for the complexing agent (thiacalix[4]arene- p-tetrasulfonate (TCAS)) to heavy-metal ions was Cu(II) > Cd(II) > Pb(II) > Ba(II). Meanwhile, higher driven voltage corresponded to a faster separation speed, while it could cause the decomposition of complexed heavy-metal ions when excessed the threshold. On the other hand, pH value would affect the hydrolysis of heavy-metal ions, the complexation of the calixarene to the heavy-metal ions and the speed of the electroosmotic flow. In our experiments, the maximum separation efficiency was achieved when the driven voltage was 1.5 V and the pH value was 5.0, corresponding to the best separation rate of 94.8%, 95.2%, 92.8%, 93.6%, for Cu(II), Cd(II), Pb(II) and Ba(II), respectively.