Adsorption of copper(II) on multiwalled carbon nanotubes in the absence and presence of humic or fulvic acids.

The adsorption of Cu(II) on multiwalled carbon nanotubes (MWCNTs) as a function of pH and ionic strength in the absence and presence of humic acid (HA) or fulvic acid (FA) was studied using batch technique. The results indicated that the adsorption is strongly dependent on pH but independent of ionic strength. A positive effect of HA/FA on Cu(II) adsorption was found at pH <7.5, whereas a negative effect was observed at pH >7.5. The adsorption isotherms can be described better by the Freundlich model than by the Langmuir model in the absence and presence of HA/FA. Adsorption isotherms of Cu(II) at higher initial HA/FA concentrations are higher than those of Cu(II) at lower FA/HA concentrations. The thermodynamic data calculated from temperature-dependent adsorption isotherms suggested that the adsorption was spontaneous and enhanced at higher temperature. Results of this work suggest that MWCNTs may be a promising candidate for the removal of heavy metal ions from aqueous solutions.