Removal of lead(II) from aqueous solution by adsorption onto manganese oxide-coated carbon nanotubes

Mn oxide-coated carbon nanotubes (MnO2/CNTs) were prepared and used to remove Pb(II) from aqueous solution. The XRD revealed that MnO2 covered MnO2/CNTs was an amorphous phase. The Pb(II) removal capacity of MnO2/CNTs decreased with the decrease of pH. From the Langmuir isotherms, maximum adsorption capacity (Q0) of MnO2/CNTs towards Pb(II) was determined (Q0 = 78.74 mg/g). Comparing with CNTs, significant improvement of Pb(II) adsorption shows MnO2/CNTs can be good Pb(II) absorbers. Although Pb(II) adsorption by MnO2/CNTs occurred rapidly within the first 15 min of contact time, contact time needed at least 2 h in order to attain adsorption equilibrium and the kinetic adsorption can be described by the pseudo-second-order rate equation. Thermodynamics of Pb(II) was studied at various temperatures of 283, 303 and 323 K and the thermodynamic parameters were also determined.