ABSTRACT Pistachio external shell (PES), cranberry (CB), and grape seed (GS) biowastes, recovered after supercritical CO 2 (SC‐CO 2 ) extraction, were evaluated as low‐cost and sustainable adsorbents for the removal of malachite green (MG) from aqueous solutions. The characterization by SEM, FT‐IR, and BET confirmed their lignocellulosic structure, and specific surface areas of 21.88 (PES), 22.73 (CB), and 1.42 m 2 g −1 (GS). Batch adsorption experiments investigated the initial dye concentration (25–250 mg L −1 ), pH (2–10), contact time (30–375 min), and temperature (25°C–45°C). Equilibrium data showed excellent agreement with the Langmuir isotherm model ( R 2 = 0.95–0.99), indicating monolayer adsorption. The maximum adsorption capacities were 121.67, 142.99, and 116.77 mg g −1 for PES, CB, and GS, respectively. PES and CB attained equilibrium within 90 min (pseudo‐first and pseudo‐second‐order models), whereas GS required 300 min (Elovich model). According to the thermodynamic analysis, PES and CB were endothermic (Δ H ° = +8.61 and +69.54 kJ mol − 1 ), whereas GS was exothermic (Δ H ° = −13.79 kJ mol − 1 ). The predominant adsorption mechanism was identified as electrostatic interaction, supplemented by hydrogen bonding and π – π stacking. Results demonstrate that SC‐CO 2 extraction of biowastes, without chemical activation, possesses considerable potential for sustainable dye removal.
Mülazımoğlu et al. (2026) studied this question.