Preparation of an activated carbon from cassava waste for the effective removal of illicit industrial food dyes: Thermodynamics and in-depth mechanism

This study reports the preparation of a low-cost and high-efficiency activated carbon from cassava residue. This novel adsorbent was tested for the removal of three industrially prohibited dyes, namely Auramine O (AO), Rhodamine B (RB), and Safranine T (ST). The separation of these dye molecules was investigated under different pH, temperature, and initial dye concentrations using the activated carbon. Characterization results showed that the cassava-based adsorbent achieved maximum adsorption capacities of 969.27 mg/g for AO, 2276.16 mg/g for RB, and 3532.14 mg/g for ST. Classical adsorption models and statistical physics theory were applied to provide an in-depth molecular-level interpretation of the dye adsorption mechanism. The results confirmed that the separation of the tested dyes is driven by endothermic physisorption, forming a monolayer on the activated carbon surface. The proposed adsorption mechanisms for the removal of AO, RB, and ST using CRAC include pore filling, electrostatic attraction, hydrogen bonding, charge transfer, and π-π stacking. Regeneration experiments demonstrated that CRAC maintained over 70% removal efficiency after five cycles. This novel activated carbon exhibits excellent cost-effectiveness and holds great promise for wastewater treatment applications in the food industry.