Eco-engineered phosphoric acid-activated carbon from Sesamum indicum seed hulls: Structure-property relationships, adsorption kinetics, and mechanistic pathways for sustainable water remediation

Abstract

An eco-friendly activated carbon was prepared from Sesamum indicum seed hulls via H3PO4 activation for the removal of Crystal violet (CV) from aqueous solutions. Characterization confirmed a porous structure enriched with oxygen and phosphorus-containing functional groups, enhancing adsorption performance. Batch experiments revealed rapid kinetics and strong dependence on pH, concentration, adsorbent dosage, and temperature. Maximum removal efficiency (~98-99%) was achieved under optimal conditions (100 mg.L-1 CV, 1 g.L-1 adsorbent, alkaline pH, 50°C). The adsorption mechanism involves electrostatic attraction, Π-Π interactions, hydrogen bonding, and surface complexation. The adsorbent retained over 60% efficiency after five regeneration cycles, indicating acceptable reusability. These findings highlight the potential of this low-cost material for sustainable wastewater treatment. The Box Behnken Design-Response Surface Methodology indicated that the adsorption rate exceeded 99.23% at an adsorbent dose of 1.5455 g.L-1, a dye concentration of 25 mg.L-1, and a pH of approximately 8.06.