Methyl Green Dye Adsorption from Wastewater Using Coconut Husk Biosorbents: Kinetic, Isotherm and Thermodynamic Studies

In this study, we prepared treated (TCH) and untreated (UCH) biosorbents from coconut husks for the sustainable removal of methyl green (MG) dye from aqueous solutions using batch adsorption mode. The products were characterized by Fourier transform infrared (FT-IR), scanning electron microscope (SEM), energy-dispersive X-ray, and N₂ adsorption/desorption methods. The performance evaluation for the MG adsorption by the adsorbents was done under different variables such as contact time, solution pH, initial dye concentration, temperature, and adsorbent dosage. The experimental data were analysed by adsorption kinetics isotherm, and the thermodynamic parameters were evaluated. FTIR, SEM, and N₂ adsorption/desorption analysis results showed that the adsorbents have functional groups, porous structure, and large surface area, suitable for adsorption. The highest percentage of 93.47 and 99.11% of MG dye were obtained by UCH and TCH, respectively, with an initial pH of 7, contact time of 60 min, adsorbent dosage of 1.0 g, initial MG concentration of 20 mg/L, and temperature of 298 K. The results of the adsorption model predicted the Langmuir isotherm could best represent the adsorption process and can best be described by pseudo-second-order kinetics. Thermodynamic parameters declared that the adsorption of the MG onto UCH and TCH is non-spontaneous, feasible, favourable, endothermic, and chemosorption. The present study showed that UCH and TCH could be cheaper, safer and more effective biosorbents for removing MG from an aqueous medium.