Multi-walled carbon nanotubes as an adsorbent material for the solid phase extraction of bismuth from aqueous media: Kinetic and thermodynamic studies and analytical applications

The present work discusses the use of multi-walled carbon nanotubes (MWCNTs) as a solid phase for removal of bismuth from aqueous media. Different factors influencing on removal efficiency were investigated carefully to get a maximum performance. The results of this study showed that most of the Bi(III) ions were removed from the solution within 30 min, at pH 0.1, and using 100 mg of adsorbent. The kinetic nature of adsorption process was analyzed using different mathematical models and that provided valuable insights into the reaction pathways and the mechanism of adsorption. The study findings revealed that the adsorption of Bi(III) ions on MWCNTs follows the pseudo-second-order kinetic model, whereas, the adsorption mechanism occurs in two consecutive steps. Various thermodynamic parameters, including the Gibbs free energy change (Delta G), enthalpy change (Delta H) and entropy change (Delta S), were calculated, and the numerical values of Delta H, Delta S and Delta G were equal to -10.02 +/- 0.6 kJ mol(-1), -24.6 +/- 0.8 J mol(-1) K-1 and -1735 +/- 0.1 kJ mol(-1) (at 293 K), respectively. The efficiency of MWCNTs for removal of Bi(III) ions from real samples was tested by extraction of bismuth from Red Sea water, wastewaters, and tap water, and the percentage of Bi(III) ions removed from these samples was in the range of 95.6-98.91% confirming suitability of MWCNTs as an adsorbent for extraction of bismuth. (C) 2016 Elsevier B.V. All rights reserved.