The Study of the Modified Grain Sorghum Stalk to Remove Methylene Blue Dye from Aqueous Solution

Pyromellitic dianhydride(PMDA) - modified grain sorghum stalk was used as a novel low-cost adsorbent to remove cationic dye methylene blue(MB) from aqueous solution. Bath studies were carried out to investigate the effects of pH and retention time on the adsorption of MB. The adsorption process could obtain >98% removal percentage within 30 minutes as the MB concentration was at 200 and 300 mg/L. And for 400 mg/L MB, 99% was removed in 6 hrs. The kinetics study showed that the adsorption processes followed the pseudo-second-order kinetic nodel, which confirming that the sorption rate is controlled by chemical adsorption. Equilibrium isotherms were analyzed by the Langmuir and Freundlich models. Langmuir model can be fitted better than Freundlich with maximum monolayer adsorption capacity of 568.18 mg/g for MB.