Biosorption of methylene blue by nonliving biomass of the brown macroalga Sargassum hemiphyllum.

The ability of Sargassum hemiphyllum to remove methylene blue (MB) from aqueous solution was evaluated. Batch experiments were conducted to examine the effects of parameters such as initial pH, contact time, biomass dose and initial dye concentration on adsorption capacity. S. hemiphyllum before and after MB adsorption was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The Langmuir isotherm model provided the best correlation with experimental data, and the monolayer biosorption capacity was 729.93 mg·g within 120 min using 0.5 g·L algal biomass and pH of 5. The pseudo-second-order kinetic model accurately described the adsorption kinetics data. Thermodynamic parameters (ΔG, ΔH and ΔS) at temperature ranges of 293-313 K demonstrated that biosorption is an endothermic and spontaneous reaction. FT-IR analysis showed that the hydroxyl, amine and carboxyl functional groups on the surface of the algae were the most important functional groups for biosorption of MB. XPS analysis indicated that the algal biomass combined with MB molecules through -NH groups. These results suggest that S. hemiphyllum is a favorable biosorbent for removing MB dye from wastewater.