Adsorption characteristic of acidified carbon nanotubes for heavy metal Pb(II) in aqueous solution

Multiwalled carbon nanotubes (MWCNTs) were acidified by concentrated nitric acid and were employed as adsorbent to study the adsorption characteristic for Pb(II) from aqueous solution. The results show that adsorption capacity of MWCNTs treated by concentrated nitric acid can be greatly enhanced. The adsorption of acidified MWCNTs to Pb(II) fits to the Langmuir model. The larger adsorption capacity of acidified MWCNTs for Pb(II) is mainly due to the oxygenous functional groups formed on the surface of acidified MWCNTs which can react with Pb(II) to form salt or complex deposited on the surface of MWCNTs. The equilibrium time of adsorption for acidified MWCNTs to Pb(II) is about 20 min, which is much shorter than that of activated carbon (about 120 min). The regeneration performance for the first time was studied, it is showed that the Pb(II) can be easily regenerated from acidified MWCNTs by adjusting the solution to pH 2.