Removal of Cd2+ from Water Containing Ca2+, Mg2+ using Titanate Nanotubes Modified by Carbon

Ca 2+ and Mg 2+ usually exist in natural water. When Cd 2+ is removed from water by adsorption, it will be inhibited by these two ions. Titanate nanotubes (TNTs) have an effective adsorption capacity for Cd 2+ due to extraordinary ion-exchange property. However, TNTs also adsorb Ca 2+ and Mg 2+ in water. In this study, carbon-modified TNT (TNT/C or TNT/HC) was synthesized by hydrothermal synthesis. The transmission electron microscope (TEM) images show that TNT/C or TNT/HC still keep nanotube morphology. The experimental results show the order of adsorption amount to Cd 2+ is TNT > TNT/C > TNT/HC when there is no Ca 2+ or Mg 2+ . But when there is Ca 2+ or Mg 2+ in the water, the order of Cd 2+ adsorption capacity becomes TNT/HC > TNT/C > TNT. It indicates that the surface carbon-modification can alleviate the hindrance of Ca 2+ or Mg 2+ to Cd 2+ removal. This is because the carbon on the surface of TNT captured part of Ca 2+ or Mg 2+ , it made more Cd 2+ be successfully absorbed by TNT through ion exchange. This mechanism was confirmed by XPS spectra analysis. The results of this paper can provide ideas for the adsorption and removal of Cd 2+ in water in the presence of Ca 2+ or Mg 2+ .