Characteristics and Methylene Blue Adsorption Capacity of Pyrochar Derived from Lemongrass Residue

In this study, the lemongrass essential oil distillation residue (LR) was the first pyrolyzed under air-controlled conditions at 500 °C for 1 hour (B500), followed by activation through alkali treatment under ultrasonic conditions at 70-80 °C for 3 hours (B5KOH). B5KOH displayed a porous architecture with heightened surface area, 79.90 m2/g, twice the specific surface of B500 material; and carbon content elevated to 87.99%. The material contained some organic functional groups such as C=O, C=C, and C-O-C. The B5KOH sample exhibited the most effective MB uptake at pH 8, achieving adsorption equilibrium within a brief timeframe of approximately 30 – 50 minutes across a concentration spectrum of MB ranging from 5 to 500 mg/L at material loadings of 1-10 g/L, qm is 74.44 mg/g. The material demonstrated substantial recyclability, maintaining nearly consistent adsorption efficiency through the fifth cycle (decreasing marginally from 96.69% to 95.13%). Experimental adsorption conformed to the Freundlich isotherm adsorption model and proceeds via a second-order kinetic model. The adsorption phenomenon was spontaneous, primarily driven by physical interactions between the B5KOH and MB molecules. Overall, lemongrass-derived pyrochar exhibited considerable promise as an adsorbent material for mitigating MB pollution.