Adsorption and Reduction of Chromium(VI) from Aqueous Solution by Multiwalled Carbon Nanotubes

The adsorption of Cr(VI) on the raw multiwalled carbon nanotubes (MWCNTs) as a function of initial Cr(VI) concentration, pH, temperature, and MWCNT dosage were studied. The removal of Cr(VI) from aqueous solution was dominated by adsorption of Cr(VI) and redox reaction of Cr(VI) to Cr(III). The adsorption of Cr(VI) decreased with increasing pH and increased with the rise in temperature and MWCNT dosage. The adsorption data of Cr(VI) on MWCNTs could be described well by Langmuir isotherm model. The thermodynamic values of Gibbs free energy ( G o ), enthalpy ( H o ), and entropy ( S ) were calculated from temperature-dependent adsorption data, and the results indicated that the adsorption of Cr(VI) on the raw MWCNTs was a spontaneous process. The results suggest that MWCNTs are suitable materials in the preconcentration and solidification of Cr(VI) from large volume of solutions.