Isotherm, kinetics and mechanistic studies of methylene blue biosorption onto red seaweed Gracilaria corticata

The present research was undertaken in order to examine the feasibility of a novel biosorbent Gracilaria corticata (red seaweed) for the removal of methylene blue (MB) from aqueous solutions. Biosorption studies were conducted as a function of equilibrium pH, initial dye concentration, and biosorbent dosage. It was identified that the biosorption capacity of G. corticata strongly depends on solution equilibrium pH and highest biosorption capacity of 28.9 mg/g was observed at pH 8. The Fourier transform infrared analysis confirmed interaction of dye molecules with binding sites on the surface of G. corticata. Also, the scanning electron microscopy images revealed morphological cell surface changes after biosorption of MB onto G. corticata. The removal efficiency of MB from solution with an initial concentration of 150 mg/L varied from 50.8 to 94.9% for an increase of the seaweed dose from 2 to 5 g/L. Kinetic study was performed using pseudo-first- and pseudo-second-order models, but higher degree of correlation coefficient and low % error values were obtained for the pseudo-second-order kinetic model. Experimental isotherms were favorable and the data were analyzed using the Langmuir, Freundlich, Redlich–Peterson, and Toth models, with the latter successfully described MB isotherm with high correlation coefficient and low % error values. The biosorption capacity of G. corticata toward MB was determined as 95.41 mg/g, according to the Langmuir model.