Characterization of multi-walled carbon nanotubes and application for Ni2+ adsorption from aqueous solutions

Abstract

Multi-walled carbon nanotubes (MWCNTs) were used to remove Νi2+ from aqueous solutions. Batch experiments performed to examine the effects of initial Νi2+ solution concentrations, pH, and contact time on Νi2+ sorption process. MWCNTs were characterized by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, micro-Raman spectroscopy, thermogravimetric analysis, and specific surface area (BET) techniques. The tested MWCNTs exhibit purity >95%, average diameter 20–30 nm, and specific surface area >150 m2/g. The results showed that 60–95% of Ni2+ was absorbed depending on the initial solution concentrations. As it is suggested by the distribution coefficient (kd) values, increased initial Νi2+ solution concentrations resulted to lower Νi2+ adsorption intensity onto MWCNTs, while the total amount of Ni2+ that removed from the equilibrating solutions increased. The adsorption of nickel onto MWCNTs was significantly affected by the solution pH; higher Ni2+ adsorption was observed at pH > 6.0. According to the contact time experiments, the sorption process reached equilibrium at 60 min. This study suggests that MWCNTs can be utilized for the removal of nickel ions from aqueous solutions and that they can be a promising candidate adsorbent for environmental applications and wastewater treatment.