Adsorption of methylene blue by a low-cost biosorbent: citric acid modified peanut shell

Peanut shell, an agricultural by-product abundantly available in China, was modified with citric acid and utilized as an adsorbent for the removal of methylene blue (MB) from aqueous solutions. Adsorption studies were conducted to evaluate the effects of pH, contact time, initial dye concentration, and temperature. The kinetic data were analyzed using pseudo-first-order and pseudo-second-order adsorption kinetic models. The results showed that the adsorption process satisfactorily fitted the pseudo-second-order kinetics. The equilibrium data for the adsorption of MB on modified peanut shells were analyzed using the Langmuir and Freundlich models. The results indicate that the Freundlich model provides a better fit of the adsorption data. Thermodynamic parameters such as the changes in Gibbs free energy (Delta G degrees), enthalpy (Delta H degrees), and entropy (Delta S degrees) have also been estimated, and the adsorption process was found to be spontaneous and exothermic. All results demonstrated that peanut shells biomass is an effective adsorbent for removing cationic dyes.