Biosorption of Methylene Blue into Pumpkin Seed: Isotherm, Kinetic and Thermodynamics Studies

Abstract

This work has demonstrated the potential utility of raw pumpkin seed shells (PSS) as a low-cost solid adsorbent for methylene blue (MB) adsorption. PSS have investigated surface functional groups with FTIR (after and before adsorption), crystal structure with XRD, and surface morphology with SEM-EDX. Biosorption parameters were examined contact time, pH, solution temperature, and initial concentration. This research was conducted to analyze adsorption processes involved in adsorption of MB onto crude PSS by gaining essential knowledge from the study of equilibrium adsorption kinetics, isotherms, and thermodynamics. It was determined whether four models-Langmuir, Temkin, Freundlich, and D-R models-fit experimental data derived from adsorption isotherms. In addition, the accuracy of fits of three models to experimental data derived from adsorption kinetics were tested, namely, the Elovich, pseudo-first order, and pseudo-second order models. Biosorption of MB on PSS is exothermic and spontaneous according to thermodynamic analysis. FTIR (Fourier transform infrared spectroscopy) studies show significant changes in the absorption values, shapes and positions of bands both before and after solute adsorption. It was found that there are two MB adsorption mechanisms: electrostatic attraction and hydrogen bonding.