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 pHpzc 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.