Adsorption behavior of heavy metal ions by carbon nanotubes grown on microsized Al₂O₃ particles

Carbon nanotubes (CNTs) were grown on the surface of microsized Al₂O₃ particles in CH₄ atmosphere at 700℃ under the catalysis of Fe-Ni nanoparticles. The CNTs on Al₂O₃ were used for adsorbing Pb²⁺, Cu²⁺, and Cd²⁺ from the solution and the results were compared with active carbon powders, commercial carbon nanotubes, and Al₂O₃ particles. The as-grown CNTs/Al₂O₃ have demonstrated extraordinary absorption capacity with further treatment or oxidation, as well as hydrophilic ability that other CNTs lacked. The adsorption capacity of CNTs on Al₂O₃ is superior to other adsorbents and the preference order of adsorption on composite Al₂O₃ is pb²⁺ > Cu²⁺ > Cd²⁺. It seemed that the adsorption of those Pb²⁺, Cu²⁺, and Cd²⁺ did not change the surface properties of composite particles. The adsorption behaviors of Pb²⁺, Cu²⁺, and Cd²⁺ by CNTs on Al₂O₃ match well with the Langmuir isothermal adsorption model and the second order kinetic model. The calculated saturation amount adsorbed by 1 g of CNTs on Al₂O₃ are 67.11, 26.59, and 8.89 mg/g for Pb²⁺, Cu²⁺, and Cd²⁺ in single adsorption test, respectively.