Terminalia catappa shell as low-cost biosorbent for the removal of methylene blue from aqueous solutions

Abstract Synthetic dyes from effluents and wastewaters can be harmful to the ecosystem even at low concentrations. This study evaluated the performance of biosorbent from Terminalia catappa (TC) shells to remove methylene blue (MB) from aqueous solutions. The biosorbent was characterized using SEM-EDX, FTIR, BET, XRF and TGA. The optimum condition for TC shell uptake of MB was at pH 5, 45 min contact time, initial concentration of 800 mg L−1 and with a maximum biosorption capacity was 88.62 mg g−1. The optimal conditions were achieved at the particle size (≤36 μm), 25 mL dye solution containing 0.1 g biosorbent dosage and 100 rpm agitation speed. The adsorption isotherm and kinetics study revealed that MB uptake was best-fit to the Freundlich and pseudo-second-order models respectively. The thermodynamic analysis determined over the temperature range of 298–318 K showed that the process was endothermic and spontaneous. The mechanism of MB uptake onto TC shells was by pore diffusion, hydrogen bonds, cation exchange, electrostatic attraction and π-π stacking. MB was effectively desorbed from TC shells using 30% acetic acid and usable for 3 cycles. The MB removal of efficiency was 90.56% in real wastewater sample at pH 5.