Durian seed adsorbents for methyl violet and malachite green adsorption: equilibrium, kinetics, and thermodynamics

This study was aimed at evaluating the removal of cationic dyes onto adsorbents derived from durian seeds. The adsorbents were prepared through different synthesis methods and characterized for surface area, surface chemistry, thermal degradation, and morphology. The adsorption performance was evaluated at different dye concentrations, contact times, and solution temperatures. The surface area of adsorbents is between 2.72 and 137 m²/g. AC-NaOH yields the highest surface area of 137 m²/g and mesoporosity of 96.3%, resulting in adsorption capacities of 1.27 and 0.703 mmol/g for malachite green and methyl violet, respectively. Hydrochar exhibits poor capacities toward malachite green and methyl violet, with values of 0.0458 and 0.0467 mmol/g, respectively. All equilibrium data obeyed the Langmuir model, while the kinetic data could be described by the pseudo-second order model. The adsorption is endothermic and spontaneous at high temperatures. To conclude, durian seed adsorbents produced via chemical activation are more effective in removing malachite green than methyl violet.