Synthesis and characterization of novel single-walled carbon nanotubes- doped walnut shell composite and its adsorption performance for lead in aqueous solutions

•A novel composite adsorbent (SWCNTs/WSh) was an effective adsorbent for Pb removal.•SWCNTs had higher Pb adsorption capacity compared to the MWCNTs, SWCNTs/Fe and CNF.•Immobilization of SWCNTs on RWSh increased its surface area from 118 to 738 m2 g−1.•TC analysis showed release of doped nanomaterials to the solution was negligible.•Adsorption isotherm followed Langmuir equation with maximum Pb uptake of 185.2 m g g−1.

In this study, first the adsorption potential of different synthesized carbon nanostructures, including single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), single-walled carbon nanotubes doped with iron (SWCNTs/Fe), and carbon nanofibers (CNFs), was compared in terms of their lead removal capacity. The results revealed that under similar conditions, SWCNTs have the most sorption capability for Pb(II) ions. A novel adsorbent, highly pure (∼99%) single-walled carbon nanotubes-doped walnut shell composite (SWCNTs/WSh), was then prepared by immobilizing SWCNT particles on the surface of walnut shell. This adsorbent was examined to evaluate its potential to remove Pb(II) ions from aqueous solutions. SWCNTs and SWCNTs/WSh composite were characterized by TEM, FT-IR, SEM and BET measurements. The effects of several parameters, such as contact time, solution pH, adsorbent dose, metal concentration, and temperature, were studied in order to find the optimum adsorption conditions. The results showed that the adsorption kinetics could be explained well by means of the pseudo second order and intra-particle diffusion models. The equilibrium adsorption isotherm followed the Langmuir equation well. The maximum Pb(II) uptake predicted was 185.2 m g g−1. In conclusion, the SWCNTs/WSh composite can be used as an effective adsorbent for the removal of Pb(II) ions from aqueous solutions.