Lemongrass (<i>Cymbopogon nardus</i>) leaves biowaste as an effective and low-cost adsorbent for methylene blue dyes removal: isotherms, kinetics, and thermodynamics studies
Rahmiana Zein, Jofi Satrio Purnomo, Putri Ramadhani, Matlal Fajri Alif, Safni Safni
Abstract
This study investigated the performance of lemongrass (Cymbopogon nardus) leaves biowaste (LLB) to adsorb methylene blue (MB) dye from an aqueous solution using the batch method. Batch experiments were conducted in order to evaluate the effect of initial MB concentration, pH, contact time, and temperature. Point of zero charge measurement demonstrated that the LLB is anionic in a wide range of pH values (pH > 6.7) that support the adsorption of cationic contaminants. The adsorption process pursued Langmuir isotherm (R2 = 0.9960) and pseudo-second-order kinetic model (R2 = 0.9960) best fitted with a maximum capacity of 43.16 mg g−1 at room temperature. The adsorption process was spontaneous and exothermic. FT-IR spectra and SEM-EDX characterization before and after adsorption affirmed the interaction of MB dye onto the LLB. It is suggested that the adsorption of the dye proceeds via electrostatic attraction, cationic exchange, π-π bonding, and hydrogen bonding, while the role of pore filling is modest. LLB has good reusability, as evidenced by four cycles of desorption using 30% acetic acid as the eluent. The optimum conditions were applied to real wastewater with a removal efficiency was 93.58% at pH 9. Therefore, the LLB could be an effective adsorbent for removing MB dye from wastewater.