Enhancing sorption capacity of methylene blue dye using solid waste of lemongrass biosorbent by modification method

Textile dye waste, such as methylene blue, has become an ecological and environmental problem. Lemongrass leaves bio-waste (LLB) has emerged as a promising alternative adsorbent for wastewater treatment. This study concerns the modification of LLB by citric acid through an esterification reaction (called as CA-LLB) to increase its adsorption capacity to remove methylene blue dye. The optimum condition for adsorption of methylene blue by LLB was achieved at pH 9, concentration 600 mg/L, contact time 45 min, and biosorbent temperature 25 °C. Whereas for CA-LLB, the optimum adsorption conditions were achieved at pH 10, concentration 1400 mg/L, contact time 75 min, and biosorbent temperature 75 °C. The methylene blue adsorption process followed the Langmuir isotherm model for LLB and CA-LLB (R2 > 0.99), which indicated the formation of a monolayer. The adsorption kinetics data for both biosorbents followed a pseudo-second-order model. Adsorption thermodynamic studies showed that the adsorption of methylene blue was spontaneous and exothermic. Boehm's titration analysis showed an increase in the hydroxyl, carboxyl, and lactone functional groups of LLB after being modified with citric acid. FTIR and SEM-EDX analysis indicated electrostatic interactions, cation exchange, and the occurrence of pore filling by methylene blue molecules. TGA analysis indicated that LLB and CA-LLB were heat stable and decomposed in three cycles. LLB and CA-LLB have good reusability using 30 % acetic acid as a desorption agent. The optimum adsorption conditions were applied to Laboratorywastewater with methylene blue removal efficiency at 95.79 % while using CA-LLB. Biosorbent modification using citric acid was proven to increase the adsorption capacity of MB from 43.1556 mg g−1 to 122.1211 mg g−1. Thus, LLB and CA-LLB have the potential to be applicative and environmentally friendly biosorbents to remove methylene blue dye in wastewater.