Adsorption of methylene blue on adsorbent materials produced from cotton stalk

Adsorbents, including cotton stalk (CS), sulphuric acid treated cotton stalk (SCS) and phosphoric acid treated cotton stalk (PCS), were used for removing methylene blue (MB) from aqueous solutions. Compared with the CS prepared activated carbons, less specific surface area and more functional groups on these adsorbents were found. The adsorption capacity was in the order of SCS > PCS > CS. It was identified that initial pH of aqueous solution had little effect on the adsorption capacity of SCS and PCS while having a great impact on the removal efficiency of CS. Maximum dye was sequestered from the solution within 120 min after the beginning of each experiment. The equilibrium data tend to fit Freundlich isotherm model for SCS and Langmuir isotherm model for PCS and CS. The kinetic data of all adsorbents followed closely by the pseudo-second-order equation and the adsorption processes are all involved in more than one single kinetic stage. The comparative study indicated that PCS and CS could be considered as potential adsorbents, and SCS as one of the best adsorbents for MB removal from aqueous solutions.