Oil industry waste derived activated carbon for Malachite Green dye adsorption: Kinetic, isotherm, and thermodynamic study

Abstract

This study explores de-oiled rice bran (DORB), an agro-industrial by-product, as a precursor for the preparation of porous activated carbon. The study assesses the performance of the synthesized activated carbon (AC) in removing malachite green(MG) dye from aqueous solutions, with a focus on developing economically viable and sustainable adsorbents for wastewater treatment. AC was synthesized using a combined thermal and chemical modification process with H₃PO₄, eliminating the need for separate activation steps. This approach reduced preparation time and energy consumption. The resulting activated carbon possessed a surface area of 465 m² g^-1 and an average pore size of 5.0872 nm. Characterization was performed using SEM, FTIR, EDAX, and pH_pzc techniques. The adsorption performance was studied under varying pH (3.0–9.0), initial MG concentration (10–50 mg L^-1), adsorbent dosage (0.1–0.6 g), contact time (0–30 min), and temperatures (303–333 K). The adsorption behaviour followed the Freundlich isotherm model, and the kinetics were well described by the pseudo-second-order model. The highest adsorption capacity was 70.92 mg g^-1. Thermodynamic analysis revealed spontaneous (ΔG<0), endothermic (ΔH>0), and favourable (ΔS>0) adsorption. Regeneration studies identified 0.2 M HCl as an effective solvent for De-oiled rice bran activated carbon (DORBAC) recovery.