Adsorption of uranyl ions from its aqueous solution by functionalized carbon nanotubes: A molecular dynamics simulation study

The adsorption behavior of uranyl ions from aqueous medium on the bare carbon nanotubes (CNTs) and CNTs functionalized with –COO−, –OH or –COOH functional groups is investigated by molecular dynamics simulations. The adsorption of uranyl ions on carboxylate ion functionalized CNT is found to be much more than that in other cases. It is also observed that the extent of adsorption on the carboxylate ion functionalized nanotube increases with the extent of functionalization. On the other hand, the maximum adsorption capacity of the –OH and –COOH functionalized CNTs are almost the same as that of the bare one. Detailed analyses demonstrate that the mode of adsorption in –COO– functionalized CNT is different from bare and –OH/-COOH functionalized CNTs. We have shown that the adsorption of uranyl ions on carboxylate ion functionalized CNTs is energetically favorable. In general, mobility of uranyl ions in the solution has been found to decrease with increasing concentration of the uranyl ions. Greater reduction in diffusivity of the uranyl ions in case of –COO– functionalized CNT as compared to other CNTs further confirms that the mode of adsorption for the carboxylate ion functionalized nanotube is different and corroborates the fact that the –COO– functionalized CNT has more adsorption capacity.