Biosorption of an anionic dye by peanut shell modified with gemini surfactants: A study on the stability of the modification and the removal efficiency

Abstract

In this study, novel biosorbents were obtained from peanut shells modified with gemini-type surfactants. Peanut shells, an agro-industrial residue, were successfully modified to enhance their naturally low biosorption capacity towards anionic contaminants. An anionic dye (tartrazine) was employed to test their performance. Three gemini were synthesized from N,N-dimethylamines with different chain length and 1,3-dichloro-2-propanol as a linker. They were purified and characterized and their surfactant properties were determined. The successful modification of the peanut shells was confirmed through a retention study based on a two-phase titration method. This method has not been reported before for modified biosorbents and should be considered to prevent risky lixiviation. Retention was found to be high (98.0–99.7%) and to be chain length-dependent. Biosorption followed the pseudo-second order kinetic model and equilibrium isotherms of the gemini-modified biosorbents were best fitted by the Langmuir model. Their maximum biosorption capacities (0.126–0.141 mmol g−1) proved to be more than threefold higher than that of the unmodified peanut shells. The retention capacity of the gemini was also tested after biosorption studies.