Multiwalled carbon nanotubes incorporated with or without amino groups for aqueous Pb(II) removal: Comparison and mechanism study

A novel amino-functionalized multiwalled carbon nanotube (MWCNTs @SiO 2 -NH 2 ) was prepared via co-condensation using etraethyl orthosilicate and 3-aminopropyl trimethoxysilane for effective removal of Pb(II) from water. The Pb (II) adsorption efficiencies of MWCNTs and MWCNTs@SiO 2 -NH 2 were compared and the change of morphology features was assessed in batch adsorption experiments. The characterization analysis like XRD, FITR and XPS revealed that amino groups were successfully grafted on the MWCNTs. Adsorption results demonstrated that the best TEOS/APTMS loading ratio was about 10:3 based on their solution volume ratio. Compared to the poor Pb(II) adsorption capacity of pristine MWCNTs, the maximum adsorption capacity of MWCNTs@SiO 2 -NH 2 was greatly improved to 147   mg/g after amination treatment. Pb(II) adsorption onto MWCNTs@SiO 2 -NH 2 was strongly pH-dependent and the optimal aqueous pH was about 5. Moreover, the pseudo-second-order kinetics model and Langmuir isotherm model could well describe the Pb(II) adsorption process by MWCNTs@SiO 2 -NH 2 . Thermodynamics analysis illustrated that the Pb(II) adsorption was spontaneous and endothermic. FTIR and XPS analysis of MWCNTs@SiO 2 -NH 2 after adsorption demonstrated the complexation between amino groups and Pb(II) played a vital role in the adsorption mechanism. Findings from the present study suggested that successful Pb(II) removal could be achieved using such novel adsorbent composite with optimized process.