Comparative adsorption characteristics of methylene blue on raw leaves and biochar of guinea grass (Megathyrsus maximus)

Methylene blue (MB), commonly found in textile wastewater systems, leads to undesirable ecological changes in the environment. Hence, removal of MB from contaminated water is a priority to safeguard the environment. This study thus aims to explore the practicability of utilizing both raw biosorbent and biochar of guinea grass (Megathyrsus maximus) for removal of MB cationic dye from synthetic contaminated water. Adsorption kinetics investigated under pre-equilibrium conditions leads to the validity of the pseudo second-order model according to linear regression analysis, with rate constants of 4.08 × 10–1 g mg−1 min−1 and 5.39 × 10–1 g mg−1 min−1, respectively, which can be attributed to the presence of two or more functional groups involved in the adsorption process. Moreover, adsorption equilibrium data of both biosorbents show the validity of the Langmuir adsorption isotherm over the Freundlich isotherm according to the linearized relationships, indicating the monolayer adsorption of MB molecules. Both raw biosorbent and its biochar exhibit more than 95% removal of MB under the optimized conditions of 0.250 g adsorbent dosage, 20 min shaking time, 20 min settling time and ambient pH of 5.60. However, the maximum adsorption capacity is much higher for the raw biosorbent as compared to its biochar. Another desirable factor is that the raw biosorbent could easily be modified to further improve adsorption characteristics. Although both biosorbent types are cost-effective, reliable, ecofriendly, well-performed and sustainable, it is more economical to use the raw biosorbent for the removal of MB from aqueous systems.