Preparation and characterization of a lignocellulosic biosorbent from cocoa pod husks (Theobroma cacao L.): optimization by Response Surface Methodology

Abstract

The valorization of lignocellulosic agro-industrial waste into low-cost adsorbents offers a promising route for treating colored textile effluents. The biosorbent was prepared from cocoa pod husks, an abundant residue in Côte d'Ivoire, through drying, grinding, sieving, and mild alkaline activation without carbonization. The preparation conditions were optimized using design of experiments, with methylene blue removal efficiency as the response—the Plackett-Burman screening of six factors identified particle size and activation temperature as the significant parameters. A central composite design applied to NaOH concentration and activation time yielded a significant quadratic model ( ; F = 26.73; p < 0.001), whose optimum (NaOH 0.96 mol L⁻¹, 5 h) predicted a removal efficiency of 96.74%, experimentally confirmed at 92.71% on average, corresponding to an adsorption capacity of about 23.2 mg g⁻¹. Physicochemical characterization (water retention, loss on ignition, FTIR, BET, SEM) confirmed the material's lignocellulosic nature, the persistence of oxygenated surface groups, and a fibrous, lamellar morphology after activation. These results show that alkali-activated cocoa pod husks constitute an effective, economical, and environmentally friendly biosorbent.