Sequestration of cadmium ions using titanate nanotube

In this manuscript, titanate (Na2Ti3O7) nanotubes synthesized from alkali hydrothermal route, with high BET surface area (206m2/g), were used as an effective sorbent to remove cadmium ions from water. Sorption capacity (qm,Langmuir=1.1mmol/g at pH 7) was higher than other sorbents. X-ray photoelectron spectroscopy (XPS) analyses performed on fresh and cadmium-sorbed samples reveal intensities of Na 1s peak decreased after sorption indicating ion-exchanging between cadmium and sodium ions occurred at interlayer of nanotubes. However kinetic study did not show a stoichiometrically equivalent amount of Na+ being released suggesting Cd uptake was not due solely to ion-exchange mechanism. Batch tests also showed that cadmium uptake was not significantly affected by variation in ionic strength, signifying cadmium ions form an inner-sphere complexation with surface hydroxyl groups. Finally, surface complexation modeling was performed based on charge distribution multisite ion complexation (CDMUSIC) model. It was found that CDMUSIC was able to fit the experimental data best when inner-sphere complexation and ion-exchange were applied together.