Effect of crystal structure on adsorption behaviors of nanosized TiO2 for heavy-metal cations

Adsorption behaviors of Pb(II) and Cd(II) ions on the nanosized titanium dioxide with different crystal structure, such as anatase, rutile, mix crystal (Degussa P25) and amorphism have been explored. The adsorption and desorption experiments of the Pb(II) and Cd(II) ions are carried out in titanium dioxide suspension under different pH value conditions. Adsorption kinetics has been studied with pH dependence isotherms, which indicates that both chemisorption and physisorption are existed in adsorption courses. The results show that the anatase TiO2 powders possess the highest chemisorption capacities among the samples, which can be attributed to its higher surface energy, rough surface and unsaturated oxygen bond. The mechanism of adsorption is suggested to be the soft acid/soft base interactions to form complexes for chemisorption and electrostatic force of electric double layer (EDL) model for physisorption.