Effect of surfactants on Pb(II) adsorption from aqueous solutions using oxidized multiwall carbon nanotubes

Batch experiments were conducted to elucidate the adsorption of Pb(II) and three types of widely used surfactants (sodium dodecylbenzene sulfonate (SDBS), octyl-phenol-ethoxylate (TX-100), and benzalkonium chloride (BKC)) from aqueous solutions by using oxidized multiwall carbon nanotubes (OMWCNTs). The effect of each kind of surfactant on the adsorption of Pb(II) and vice versa were studied in detail. The results indicated that the pH values affected the adsorption of Pb(II), TX-100 and BKC to OMWCNTs dramatically, whereas the adsorption of SDBS was almost pH-independent at pH < 9 and then decreased with increasing pH at pH > 9. The adsorption of Pb(II) was enhanced obviously by the presence of SDBS, but slightly inhibited by the presence of BKC. The adsorption of Pb(II) can be well described by Langmuir model. The adsorption process in the Pb-surfactant-OMWCNT ternary system was attributed to electrostatic, hydrophobic and π-π interactions. XPS analysis showed that the adsorption mechanism was mainly due to chemical interaction between Pb(II) and the surface functional groups of OMWCNTs and the surfactants.