Sustainable corncob waste-derived activated carbon through one-step pyrolysis and chemical activation with KOH for efficient rhodamine B adsorption

Rhodamine B (RB) in wastewater poses serious health and environmental risks due to toxic and carcinogenic nature. Adsorption of RB using biomass-based Activated Carbon (AC) offers a cost-effective, efficient, and environmentally friendly solution. Therefore, this study aims to convert corncob waste into AC using a one-step pyrolysis technique combined with chemical activation using KOH. AC was synthesized at various temperatures and characterized to determine the physicochemical properties. The RB adsorption performance was assessed through batch experiments under varying operational parameters, including initial concentration, contact time, pH, and adsorbent dosage, as well as the effects of interfering ions and real water samples. The results showed that AC synthesized at 800 °C (AC-800) had a porous structure with a high Specific Surface Area (SSA) of 1347 m²/g and demonstrated excellent adsorption performance for RB. The AC-800 adsorbent achieved a maximum adsorption capacity of 101.01 mg/g, with adsorption isotherms fitting well to the Langmuir model. Adsorption kinetics followed the pseudo-second-order (PSO) model, with a removal efficiency of 97.35 % for RB. Furthermore, mass transfer during the adsorption process was examined using the Boyd model, along with the external mass transfer model. Analysis of thermodynamic parameters indicated that the RB adsorption process was spontaneous and heat-absorbing (ΔH° = 18.85 kJ/mol). Although the presence of interfering ions and real water matrices affected AC-800 performance, significant RB removal was still achieved. The adsorption mechanism was likely controlled by hydrogen bonding, π–π interactions, and pore filling. AC also showed good regeneration and reusability potential after multiple adsorption cycles, suggesting high effectiveness and sustainability as an adsorbent for the RB elimination from wastewater.